JPH0428865A - Production of refractory metal silicide target - Google Patents

Abstract

PURPOSE:To produce the target having superior uniformity and high density by keeping a specific pressure until silicide reaction is finished, and raising this pressure up to the desired pressure after the reaction is finished at the time of subjecting a powder mixture of refractory metal and silicon to hot pressing treatment. CONSTITUTION:A high purity graphite mold is filled with a powder in which refractory metal (W, Mo, etc. <= about 50mu grain size) and silicon (<= about 150mu grain size, <= about 5ppm ferrous impurities, <= about 1000ppm oxygen) are mixed in the prescribed molar ratio. Subsequently, hot pressing treatment is performed in vacuum atmosphere (about 1X10<-3>-1X10<-5>Torr) at about 900-1300 deg.C under a pressure of <= about 50kg/cm<2> until silicide reaction is finished. When silicide reaction is finished, the pressure is raised up to the desired pressure at 1-20kg/cm<2>/min pressure rise rate and hot pressing treatment is carried out at about 1300-1250 deg.C. By this method, the refractory metal silicide target useful for forming a gate electrode film for MOS-LSI can be obtained.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a method for manufacturing a high melting point metal silicide target. The present invention relates to a method for manufacturing a metal silicide target.

[Conventional technology]

Conventionally, electrodes or wiring of semiconductor devices, especially MO
The gate electrode of the 3-LSI is made of polysilicon (p-8i
) have been widely used.

However, as LSIs become more highly integrated, electrical signal transmission delays become a problem, and electrode materials with low electrical resistance are required. Refractory metal silicides are widely used.

Such gate electrode films of high melting point metal silicide are mostly formed by sputtering, but the properties of the film are heavily influenced by the characteristics of the target material, and in particular, the uniformity of the target material is influenced by the film composition and film composition. This is a very important factor as it relates to the uniformity of thickness.

The target material made of such a high melting point metal silicide is obtained by hot pressing a mixed powder of silicon and a high melting point metal such as tungsten (W), molybdenum (MO), tantalum (Ta), or titanium (Ti). It is obtained by

The above method has a simpler manufacturing process than a method in which a mixed powder of a high melting point metal and silicon is fired to form a silicide, and the powder obtained by pulverization is hot-pressed, and there is no possibility of contamination with impurities from the process. Since the amount is small, high-purity products can be manufactured economically.

[Problem that the invention seeks to solve]

However, in the above method, silicon with a low melting point melts instantaneously due to the heat generated by the silicidation reaction, and the molten silicon is applied to defects and low density areas inside the sintered body due to the pressure of the hot press. As a result, there were problems with uniformity, such as formation of fibrous platelets and partial formation of a Si-rich structure (texture unevenness) in low-density areas along the pressure distribution.

For example, in the case of a tungsten silicide target, the composition of the tungsten silicide target for forming the gate electrode of MO8-LSI is usually Si/W=2°2-3.
．． The molar ratio of WSi2 is often used, and silicon is contained in excess of the stoichiometric composition of WSi2.

When tungsten powder and silicon powder are mixed and subjected to hot press treatment, the treatment temperature is
A temperature of 1370 to 1400°C, which is slightly lower than the eutectic temperature of i, is used. When hot-pressing at such a temperature, the tungsten powder and the silicon powder react during the heating process, and an intermetallic compound (silicide) of WSi2 is formed without generating a large amount of heat.

The temperature at which this silicidation reaction occurs is usually 100
0 to 12006C, but it is mainly influenced by the surface oxide film of the tungsten powder and silicon powder, and the reaction temperature tends to be lower as the oxygen content is lower (the surface oxide film is thinner). The melting point of WSi2 formed in the reaction is 2165
°C, whereas the melting point of silicon is as low as 1410 °C, the temperature of the sintered body instantaneously exceeds the melting point of silicon due to the heat of reaction. As a result, the remaining molten silicon that has formed WSi2 through the reaction is pushed out into defective areas and low-density areas of the sintered body by the pressure of the hot press, resulting in fibrous platelets and uneven structure. Such steel plates and the like tend to occur more easily as the amount of excess silicon increases and as the reaction temperature increases. A similar trend is also observed, as the more rapid the reaction, the greater the instantaneous temperature rise.

[Means for solving problems]

Therefore, the inventors of the present invention have conducted intensive studies to solve these problems, and have found that when hot-pressing a mixed powder of high-melting point metal and silicon, no pressure is applied until the silicidation reaction is completed. If the pressure is applied at a very low pressure and then the pressure is increased to the target pressure after the reaction and hot press treatment is performed, silicidation has already been completed, so there is no generation or movement of molten silicon during pressurization. The inventors have discovered that the problematic rope plates, etc. do not occur, and have arrived at the present invention.

That is, an object of the present invention is to provide a method for manufacturing a high-melting point metal silicide target with good uniformity and high density by solving the problem of silicon fibrous steel plates and uneven structure.

The purpose is to hot press a mixed powder of a high melting point metal and silicon to produce a high melting point metal silicide target, and the pressure is about 50 kg/cIII' or less until the wrinkle cidation is completed. This can be easily achieved by a method for producing a high-melting point metal silicide target, which is characterized in that hot press treatment is carried out at a temperature of 100 mL, and after the completion of the reaction, the pressure is increased to a target pressure and hot press treatment is carried out.

The present invention will be explained in detail below.

In the present invention, a high melting point metal is used which has a melting point higher than the melting point of silicon and which undergoes an exothermic reaction with silicon to form a silicide.

Specifically, tungsten (W), molybdenum (Mo)
, tantalum (Ta), titanium (Ti), and other high-melting point metals, especially tungsten (W) or molybdenum (
MO) is preferably used.

On the other hand, silicon is not particularly limited, but high purity silicon with low oxygen content is preferred.

Each of the above components is used in powder form, but in the case of high melting point metals, it is usually best to use particles with a particle size of 50 μm or less, preferably 20 μm or less, and in the case of silicon, particles with a particle size of 150 μm or less are used. Hereinafter, it is preferable to use a material having a diameter of 1 to 55 μm.

When using commercially available high-purity silicon powder,
Often, iron-based impurities mixed in from containers and jigs during grinding and oxygen due to surface oxidation are removed by several hundreds of particles each.
Since it contains about 11,000 ppm), it is necessary to remove the oxygen-rich fine particles using a classifier and to remove iron-based impurities and surface oxide film by acid cleaning. Iron-based impurities are 10 ppm or less, oxygen is 11,000 ppm or less, preferably iron-based impurities are 5 ppm or less, and oxygen is 600 ppm or less.
It is preferable to keep it below ppm.

Similarly, the high melting point metal should preferably be of high purity and contain little oxygen; for example, it is preferable to use a commercially available 4N or higher metal.

In the present invention, first, the above-mentioned high melting point metal powder and silicon powder are weighed and blended in a desired molar ratio, and then dry mixed using a ball mill or the like.

Compared to firing the silicon powder in the open in a crucible, the silicon powder is filled in the mold in hot press processing, so there is less loss due to evaporation (therefore, correction of the blended molar ratio is usually not necessary). However, it is preferable to increase the blending molar ratio by 0 to 1%.

To prevent contamination from containers, balls, etc., it is best to use a mixing method that is lined with nylon, or one that is made of the same metal as the high-melting point metal used, its silicide, or molybdenum material. . The atmosphere during mixing is preferably an inert gas atmosphere such as nitrogen or argon, or a vacuum atmosphere; in either case,
It is necessary to prevent contamination by moisture.

In the present invention, the mixed powder obtained as described above is filled into a high-purity graphite mold and hot-pressed to produce a target material. The pressure is controlled before and after the silicidation reaction.

The atmosphere for the hot press treatment may be an inert gas atmosphere such as nitrogen or argon, preferably a vacuum atmosphere in order to evaporate and remove impurities. The degree of vacuum is preferably higher, usually 1 x 10 '-' ~ I
It is sufficient if it is 0-5 torr.

The pressure of the hot press treatment is approximately 50 kg/cnf or less, preferably 20 kg until the silicidation reaction is completed.
/cTl or less, and after the reaction is completed, the pressure is increased to the desired pressure for sintering.

There are no particular restrictions on the method of pressurizing until the silicidation reaction is completed; for example, the above pressure is applied from the beginning, or the pressure is applied for a short period of time to about 100 to 200 kg/cm, and then immediately A method such as applying contact pressure to change the pressure to the above-mentioned pressure may be adopted. In either case, it is desirable that the top surface of the filled mixed powder be flat. If the pressure before the end of the silicidation reaction is too high beyond the above range, molten silicon will move and segregate during the silicidation reaction.
The intended purpose of the present invention cannot be achieved.

On the other hand, the pressure after the silicidation reaction is not particularly limited as long as it is a high pressure, and a higher pressure is advantageous for higher density. In practice, it is determined by the strength of the molding material, and when using graphite molds, it is usually 15 C1-350kg/
cri, preferably 200-350 kg/crl
The range of

The pressure increase after the completion of the silicidation reaction is carried out at a time when the temperature increased by the reaction heat is absorbed by the graphite mold, and the temperature drops below the melting point of silicon, and when there is no more molten silicon.

The silicidation reaction is fast, or the furnace temperature is high, so it takes time to dissipate the heat, and it is usually advisable to start increasing the pressure after the reaction is maintained for 3 to 60 minutes, preferably 15 to 60 minutes. If the timing of pressure increase is delayed too much, sintering will proceed too much, which is disadvantageous to high density.

In addition, the rate of pressure increase is 1 to 20 kg/crl/
min.

Preferably it is 5 to 15 kg/car/min.

The temperature of the silicidation reaction varies depending on the type of high melting point metal, the particle size distribution of the high melting point metal powder and silicon powder, the surface oxide film, etc., but is usually in the range of 900 to 1300°C.

When the silicidation reaction occurs, the temperature rises instantaneously due to the heat of the reaction, and metal vapor, oxide vapor, and degassing are generated. Also, if even a small amount of pressure is applied, contraction is observed in the vicinity. . Therefore, the progress of the silicidation reaction can be judged from changes in the degree of vacuum or changes in shrinkage displacement due to steam and degassing.

The temperature of the hot press treatment after the completion of the silicidation reaction is MS i x (M=W, Mo, Ti.

A temperature slightly lower than the eutectic temperature of Si (such as Ta) and Si is used, and is usually 1300 to 1450°C.

In the case of tungsten silicide, 1370~
1400℃, 1380 for molybdenum silicide
It is preferable to set the temperature to 1410°C.

The temperature is generally raised at a rate of 1 to 20°C/min, but it is preferable to gradually raise the temperature in the temperature range of 900 to 1300°C where the silicidation reaction occurs. Specifically,
It is preferable to set the temperature increase rate to 5°C/min or less.

The hot press treatment time is sufficient to soak the entire sintered body, and although it depends on the size of the sintered body, it is usually 0.
．． It is said to be in the range of 5 to 3 hours.

〔Example〕

EXAMPLES Hereinafter, the present invention will be explained in more detail with reference to examples, but the present invention is not limited to the following examples unless it exceeds the gist thereof.

Example 1 The following materials were used as raw materials.

(a) Si powder Commercially available high-purity Si powder (-300 mesh) is treated with an air classifier to remove oxygen-rich fine powder and coarse powder with poor sinterability, and further purified to obtain high purity. Si powder (oxygen content 220 ppm) was used.

The Si powder was purified by first treating it with a 6N-HC1 aqueous solution at 60°C, then with a 0.5N-HF aqueous solution to dissolve and remove Fe-based impurities and oxides contaminated during pulverization, and then with pure water. It was washed repeatedly and finally dried under vacuum at 80°C.

(b) W powder Commercially available 5N high purity W powder (average particle size 4 μm, oxygen content 34
0 ppm) was used.

Using each of the above raw materials, W
:5i=1:2.7 ratio for 4 hours and 10.
4 kg of mixed powder was obtained.

Note that a nylon-lined iron ball was used as the mill ball.

The above mixed powder was filled into a high purity graphite mold with an inner diameter of 280φ in a large hot press furnace, and hot press treatment was performed in a vacuum atmosphere.

The processing pressure was 16 kg/cJ up to 1250°C.
After holding at 50°C for 1 hour, the pressure was increased to 200 kg/crl. The silicidation reaction occurred 7 minutes after reaching 1250°C. This reaction temperature is higher than usual, but this is due to the difference between the ambient temperature being measured and the temperature of the sintered body in the graphite mold.

The pressure was increased at a rate of 13 kg/cnf/min.

In addition, the temperature increase rate is 5°C/min up to 300°C,
10°C/m in the range of 300~125'0°C/min
in.

In the range of 1250 to 1395°C, the rate was 5°C/min.

The final holding temperature and time were 1395°C for 3 hours.

In addition, before the silicidation reaction, the sintered body was held at 1050°C for 1 hour in order to uniformly heat the entire sintered body.

The density of the hot-pressed product obtained as described above was 7.89 g/crl.

The upper and lower surfaces of the hot-pressed product were ground by 0.5 to 1 mm, and the Si braided steel plate was inspected for defects using an ultrasonic inspection and imaging device manufactured by Hitachi Construction Machinery Co., Ltd. As a result, it was found that the hot press-treated product of the present invention had a reduced defect rate and improved uniformity compared to conventionally processed products.

The structure was also found to be uniform and good when observed using a metallurgical microscope.

Furthermore, a disk of 75φ×6t was cut out from the hot-pressed product, and a copper backing plate was bonded to the back surface to prepare a target. This was sputtered using a sputtering device manufactured by Shimadzu Corporation, and the presence or absence of a Si braided rope plate-like surface was observed from the surface of the two lotions. As a result, no such pattern was observed in the hot-pressed product of the present invention, and the product was uniform.

Table 1 shows the comparison results between the product of the present invention and the conventional product.

Table ■ [Effects] According to the present invention, when hot-pressing a mixed powder of high-melting point metal and silicon, the conventional problems can be solved by a simple method of controlling the pressure before and after the silicidation reaction. A high melting point metal silicide target with good uniformity can be obtained by solving problems such as silicon wire plates and structure unevenness.

Claims (1)

[Claims] (1) When producing a high melting point metal silicide target by hot pressing a mixed powder of high melting point metal and silicon, the hot press is applied at a pressure of about 50 kg/cm^2 or less until the silicidation reaction is completed. A method for producing a high melting point metal silicide target, which comprises performing a press treatment, and after the completion of the reaction, increasing the pressure to a target pressure and performing a hot press treatment.